Mid-2011 27" iMac Recently I've noticed the following two symptoms of defective audio: 1. The Left Hand speaker tends to buzz according to the strength of the audio signal. For instance a voice will tend to buzz more on stressed syllables. 2. After watching a substantially long video, perhaps 40 mins or more, on Youtube or VLC Player, for instance, a residual hum remains for some time even when no audio signal is present, and audio apps, in this case VLC Player, are closed. It seems to me that the speaker has become physically damaged somehow. Perhaps a rogue signal passed through at some point and killed it off. Anyone had experience of this or any suggestions of what to do? Possibilities of a repair? I am outside my Applecare protection.